In particular, hereafter reference shall be made to mounts of the type usually used for example in machine tools for supporting and orienting a rotary head or else a rotary table. In other examples, such mounts are used to displace or angularly position a member of a machine with respect to another, for example the mount can be used in marble machines, machines for joinery, manipulators, etc.
Currently there are two types of chip machines: continuous treatment machines and discontinuous treatment machines.
The first (i.e. continuous treatment machines) are equipped with a treatment head or workpiece-carrying table the position and mutual orientation of which can be modified continuously by stepper motors controlled by the electronics of the machine. Machines of this type allow even very complex treatments to be carried out but, however they have drawbacks which in practice limit their use above all to very coarse treatments. Indeed, continuous treatment machines, during operation, generally have high vibration, low chip removal and, therefore, long treatment times. Moreover, continuous treatment machines are usually very expensive and are not very strong and a limited resolution. Usually the maximum resolution that can be obtained with a continuous treatment machine is equal to 0.001°.
Discontinuous treatment chip machines, on the other hand, are made using Hirth mounts. Hirth mounts have two identical disks, equipped with face teeth connected together engaging the respective teeth between them. The disks can be rotated with respect to each other before connection so as to be positioned as required by the treatment being carried out and, therefore, so as to position as desired the mechanical member connected to them, usually consisting of the workpiece-carrying table or else the treatment head. The mounts of the type indicated are widely used in practice since they allow the machine members to be positioned as required for the particular treatment being carried out and the connection between the disks is strong and precise enough to be used even for calibrated positioning.
Machines which use Hirth mounts are usually strong, they are not affected by vibrations and they allow large quantities of chips to be removed at each run. However, they are not very flexible and their use becomes all the more difficult, up to the point of becoming practically impossible, when very high resolutions are desired. Indeed, the resolution which can be obtained with conventional mounts of this type becomes greater as the number of teeth on the disks (of the same type) becomes greater. This is due to the fact that the disks have the same number of teeth and, therefore, the greater the number of teeth, the greater the number of positions in which a disk of 360° is divided (the positions are defined, for example, by the gaps between two teeth of a disk in which the teeth of the other disk engage). This necessarily implies that to obtain greater resolution and, therefore, to divide the 360° angle into many positions it is necessary to increase the number of teeth. Moreover, it must be considered that the teeth must transmit torque and, therefore, their thickness cannot be too thin otherwise they would be too weak and there could be the risk, if subjected to too high forces, of them breaking.
Of course, these two drawbacks combined with each other mean that in practice as the required resolution increases the diameter needed for the disks increases and, therefore, the bulk, the weight, etc. increases.